When to Plant Lettuce in San Juan County, CO
Lettuce is a fast-growing cool-season green available in leaf, romaine, butterhead, and crisphead types. It is the foundation of salads and one of the easiest crops to grow.
San Juan County, Colorado is in USDA Zone 4a. The average last spring frost is June 18 and the first fall frost is September 8, giving you a growing season of approximately 82 days.
At an elevation of 7,539 feet, San Juan County receives approximately 20.1 inches of rainfall annually with predominantly loam soil. Summer highs average 82°F, so choose short-season varieties of Lettuce to ensure they mature before fall.
San Juan County Soil Profile
Soil Type
Loam
Soil pH
6.3-8
Drainage
Well Drained
Plant Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Soil Compatibility in San Juan County
How your county's soil matches Lettuce's growing requirements.
Soil pH
Your soil pH (6.3–8.0) is more alkaline than Lettuce prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in San Juan County is excellent for Lettuce — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Lettuce.
Organic Matter
Organic matter is moderate (2.5%). Annual compost additions will help Lettuce.
How to Plant Lettuce
Fall planting: Sow 12 weeks before your first frost date for a fall harvest.
Succession Planting Lettuce
Sow every 3.4 weeks. Last sowing by Jul 10 to harvest before frost.
For a dedicated fall crop, sow by Jun 16.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Lettuce
Lettuce needs approximately 0.7 inches of water per week (3" per month). Here's how your county's rainfall compares month by month.
| Month | Lettuce Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.4" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 1.6" | 0" | ❄️ Dormant |
| Apr | — | 2" | 0" | ❄️ Dormant |
| May | — | 2.4" | 0" | ❄️ Dormant |
| Jun | 3" | 1.6" | 1.4" | 💧 Light watering |
| Jul | 3" | 2" | 1" | 💧 Light watering |
| Aug | 3" | 2.3" | 0.7" | 💧 Light watering |
| Sep | 3" | 1.6" | 1.4" | 💧 Light watering |
| Oct | — | 1.6" | 0" | ❄️ Dormant |
| Nov | — | 1.3" | 0" | ❄️ Dormant |
| Dec | — | 1.1" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Jun–Sep in San Juan County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Lettuce Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Lettuce Planting Timeline — San Juan County, CO
Lettuce Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | May 7 | May 7 – May 21 |
| Transplant Outdoors | June 18 | Jun 18 – Jul 2 |
| Direct Sow | June 11 | Jun 11 – Jul 2 |
| Harvest | July 23 | Jul 23 – Oct 1 |
| Fall Sowing | June 16 | Jun 16 – Jun 30 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | — |
| May | Start Indoors |
| June | Transplant Outdoors Direct Sow Fall Sowing |
| July | Transplant Outdoors Direct Sow Harvest |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
0.7"/week · Natural rainfall sufficient
📅 Days to Maturity
30–60 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 4a
📆 Growing Season
82 days in San Juan County
Growing Tips for Lettuce in San Juan County
Direct sow Lettuce outdoors after June 18 in San Juan County when soil has warmed and frost danger has passed.
Common pests for Lettuce in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Sow seeds directly every 2 weeks for continuous harvest. Provide afternoon shade in warm weather to delay bolting. Harvest in the morning for crispest leaves.
Recommended Lettuce Varieties for San Juan County
Fast-maturing leaf and butterhead types
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Very easy to save. Let a few plants bolt each season.
Lettuce in Other Locations
Frequently Asked Questions
When should I plant Lettuce in San Juan County, CO?
San Juan County is in Zone 4a with an average last frost of June 18. Plan your Lettuce planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Juan County, CO?
San Juan County, Colorado is in USDA Hardiness Zone 4a. The average last spring frost is June 18 and first fall frost is September 8.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help San Juan County gardeners in Zone 4a organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.